Eating large quantities of cured meats like bacon could damage lung function and increase the risk of lung disease.

A Columbia University team found people who ate cured meats at least 14 times a month were more likely to have COPD - chronic obstructive pulmonary disease.

COPD, which includes chronic bronchitis and emphysema, kills around 30,000 people in the UK each year.

The report, in the American Journal of Respiratory and Critical Care Medicine, said nitrites in meat may be to blame.

However, the overall risk of developing COPD remains low.

Nitrites generate reactive nitrogen species that may cause damage to the lungs

Dr Rui Jiang

Dr Rui Jiang, leading the research, said high levels of nitrites are used in cured meats such as bacon as preservatives, anti-bacterial agents and colour fixatives.

He said reactive nitrogen species, molecules that can damage body tissues, might be the key.

He said: "Nitrites generate reactive nitrogen species that may cause damage to the lungs, producing structural changes resembling emphysema."

COPD risk

The researchers looked at 7,352 American individuals who participated in the Third National Health and Nutrition Examination Survey, conducted between 1988 and 1994.

They compared the results of lung function tests and the risks of developing COPD in participants and found those who ate the meats more often had worse lung function and were more likely to have COPD.

COPD is a term used for a number of conditions, and results from chronic bronchitis and emphysema, two inflammatory lung diseases.

It leads to damaged airways in the lungs making breathing more difficult, and is a major cause of disability and death.

Diet 'not to blame'

The researchers also found individuals who consumed cured meats frequently were more likely to be male and of a lower socio-economic status, and to smoke, than those who never consumed cured meats.

They also often had lower intakes of vitamin C, fish, fruits and vegetables, and higher energy intakes.

Yet they concluded these factors were not to blame for the effects on lungs.

COPD kills around 30,000 people in the UK every year

Dr Jiang said: "Adjustment for these factors in our analyses did not appreciably change our findings."

He said the link between cured meats and lung function was therefore unlikely to be explained by these other dietary factors.

He called for more studies of high dietary nitrite intake to assess whether it is a risk factor in the development of COPD.

Professor Peter Calverly of the British Thoracic Society said: "This study illustrates that factors other than smoking may contribute to COPD.

"Although smoking remains the single most significant cause of COPD this research seems to suggest other factors may result in increased risk of the disease."